1. Field of the Invention
The present invention relates to an insert molding method and a metal mold for insert molding. More particularly, the present invention relates to a method of manufacturing a molded product having inserts in a layered state.
2. Related Art
Various methods have been suggested for securing inserts to a predetermined position when manufacturing a molded product having inserts which are integrally embedded into the molded product.
For instance, Japanese Patent Application Laid-Open No. 7-88882 discloses a method for solving problems which arise in manufacturing a molded product. FIG. 9A is a sectional view of a switch box A provided with a connector unit .alpha. outside.
Reference character .gamma. indicates a bus bar for electrically connecting the upper terminal of the connector unit .alpha. to a switch box unit .beta.. Reference character .delta. indicates a bus bar for electrically connecting the lower terminal of the connector unit .alpha. to the outside of the switch box A.
The switch box A is obtained by inserting bus bars .gamma. and .delta., in advance, into a cavity E formed by an upper metal mold B, a lower metal mold C, and a slide metal mold D, as shown in FIG. 9B, and then injecting resin into the cavity E. Here, the bus bar .gamma. is held between a convex portion C1 on the lower metal mold C and the upper metal mold B.
In the prior art, however, other bus bars cannot be held in a position parallel to the bus bar .gamma. in a layered state to electrically connect the lower terminal of the connector unit .alpha. to the switch box unit .beta.. If the bus bar cannot be held during insert molding, there might be a collision between inserts inside the molded product. This makes the molded product unreliable, and contacts cannot be maintained at necessary positions inside the switch box.
To eliminate the above problem, Japanese Patent Application Laid-Open No. 7-88882 discloses a method in which the connector unit .alpha. is provided outside the switch box A, and bus bars are disposed in such positions that they are in parallel with the bus bar .gamma. when a separate component .zeta. having a separately-made terminal .epsilon. as an insert (shown in FIG. 9C) is inserted into the connector unit .alpha. later on.
In such case, however, the slide metal mold is necessary, and to obtain one product, insert molding has to be performed twice, making the manufacturing process very complicated. The above method has a further disadvantage in that since the separate component .zeta. is inserted into the connector unit .alpha. later on, it tends to come off when disconnecting the connector unit .alpha. from a mating connector.
According to the above method of the prior art, no convex portion like the convex portion C1 can be formed on the metal mold when it is necessary to maintain a water resisting property in some degree. In such case, there is no way to arrange bus bars at predetermined positions.
In the case where the inserts are bus bars which need to be electrically connected, the slide metal mold D as shown in FIG. 9B is necessary for preventing resin from adhering to the surface that should remain exposed. Such method of the prior art has disadvantages in that the slide metal mold D results in high production costs and tends to break down in the molding process.